The abovenoted guiding sleeves of plastic material or metal are inserted into the back rests of the seats from above. They allow the slidable accommodation of a rod of a headrest so that the height of the headrest can be adjusted accordingly. As a result of a corresponding frictional engagement or releasable lock-in position, the headrest can be adjusted to the desired height each time. According to safety regulations, the headrest for security reasons must not be removed from the back rest under a corresponding load.
From German Patent DE 33 01 073 a guiding sleeve has become known which, on the one hand, provides a safe locking mechanism for preventing the rod from being removed and, on the other hand, allows a simple and effective unlocking control. This is realized in that the sleeve bore at the upper end includes an extension which receives an elongated spring element. A long front side of the spring element cooperates with the rod of the headrest and with a long rear side which is supported by the wall of the extension. In the extension an unlocking element is arranged comprising two parallel spaced legs which with their ends cooperate with the ends of the spring element, while being located at the side of the sleeve bore, and are movable from a grip to the spring element and towards the longitudinal extension.
The known guiding sleeve necessitates that an abutment in the form of a notch or the like is arranged on the rod in the direction of load. Consequently, the rod needs to be dimensioned accordingly so as to withstand the prescribed load. Moreover, the notch needs to be dimensioned at a sufficient depth so as to ensure a safe abutment preventing the rod from being removed. Finally, the stop spring provided for use with the known guiding sleeve involves a relatively great expense for production.